121.20.584.00 by Danfoss

The 121.20.584.00 is a hydraulic unit supplied by Danfoss for compact fluid-power applications. It uses a positive-displacement layout to move hydraulic fluid in a controlled manner, making it suitable for equipment that needs predictable flow and pressure behavior during operation. This corrects the inconsistent soft-starter wording in the source material, because the listed operating data clearly describe a hydraulic assembly rather than an electrical motor-start device. The compact housing also helps simplify installation because the hydraulic ports and mounting features are grouped on one face, which can reduce routing complexity in tight machine spaces.

At the core of the unit is a displacement of 8.4 cm³/rev, which determines how much fluid is moved during each shaft revolution. The shaft can operate at speeds up to 4000 rpm, and the lower operating limit is 700 rpm for slower cycles. When driven at maximum speed, the theoretical flow reaches 33.6 L/min. The housing tolerates transient peaks of 280 bar, and the case-drain path returns internal leakage fluid through a 1/4 G drain port so pressure does not build inside the unit. A 1:8 tapered shaft end supports keyed couplings, while a 36.5 mm pilot and four through-holes help center and secure the mounting flange.

For continuous duty, the internal passages are rated for 250 bar working pressure. The unit supports bidirectional rotation, so the same assembly can be used where shaft direction must reverse during operation. The shaft end uses an M12 × 1.25 retaining thread to secure the driven hub, and the total mass is 2.5 kg, which keeps the assembly relatively light for machine mounting. Matching inlet and outlet geometry with 13.5 × 30 × M6 port dimensions can simplify hose selection, and the flange layout supports stable installation on compatible hydraulic equipment.